The invention relates to seamed fabric for use in the press section of a papermaking machine.
Paper is conventionally manufactured by conveying a paper furnish, usually consisting of an initial slurry of cellulosic fibers, on a forming fabric or between two forming fabrics in a forming section, the nascent sheet then being passed through a pressing section and ultimately through a drying section of a papermaking machine. In the case of standard tissue paper machines, the paper web is transferred from the press fabric to a Yankee dryer cylinder then creped.
Paper machine fabric or clothing is essentially employed to carry the paper web through these various stages of the papermaking machine. In the forming section, the fibrous furnish is wet-laid onto a moving forming wire and water is encouraged to drain from it by means of suction boxes and foils. The paper web is then transferred to a press fabric that conveys it through the pressing section, where it usually passes through a series of pressure nips formed by rotating cylindrical press rolls. Water is squeezed from the paper web and into the press fabric as the web and fabric pass through the nip together. Press fabrics generally comprise a batt of fibers needled to a base fabric. In the final stage, the paper web is transferred either to a Yankee dryer, in the case of tissue paper manufacture, or to a set of dryer cylinders upon which, aided by the clamping action of the dryer fabric, the majority of the remaining water is evaporated.
The base fabrics of press felts are woven endless, whether they are seamed or not, such that the yarns of the weft in the loom lie in the machine direction of the fabric on the paper machine. The weft yarns weave back and forth continuously between the laterally extending edges of the fabric and form a seam loop at the reversals on one side. The two ends formed are then joined together on the machine by means of a pintle wire.
Press felts consist of multiple layers which are secured together by needling. This works by mechanically locking the constituent batt fibers into various layers and in so doing holds them together. In addition, the batt fiber gives a homogenous paper support surface. Due to the method of base fabric manufacture, the area around the seam is free of cross machine direction (CD) yarns. This means that the ability of the batt fiber to become anchored in this region is much reduced, and the anchoring achieved much less effective than in the main area of the felt. Also, due to the greater void volume in the seam area, in comparison to the main body of the fabric, the propensity to marking of the paper sheet is greatly increased. Efforts to address this problem include those described in U.S. Pat. No. 5,466,339 where extruded monofilaments are secured to the underside of the fabric in the machine direction. These extruded monofilaments help to express water but the extrusion process is expensive and time consuming.
The need remains for a solution to issues with the seam area of a seam felt with reduced cost and without special protection for the seam loops.